The present invention relates generally to the beneficiation of feedstocks used in the refinery industry for preparing fuels and the like. More particularly, it is concerned with a new and improved process for reducing the nitrogen content of such fuel feedstocks by removal of basic nitrogen compounds from hydrocarbonaceous fluids obtained from various sources.
It is known in the industry that feedstocks used for preparing fluid fuels have contained varying amounts of hetero atom impurities and that such impurities have been a major problem for fuel refineries necessitating large capital outlays to handle the myrid of problems generated by the presence of such material. The major heteroatom impurities present in these fluid feed streams are sulfur, nitrogen and oxygen. Sulfur has created one of the more serious problems because of the resultant air pollution that occurs when sulfur-bearing hydrocarbon fuels are burned. Among the heteroatom impurities sulfur is the most easily removed and various means already have been developed and implemented for the control of that material. Oxygen typically is of little concern except for the small amount of phenolic compounds present in cracked gasolines. These impurities are removed primarily to improve the stability of the gasoline product, principally the discoloration of the fuel that occurs as result of their presence.
While nitrogen does not create as serious a pollution problem as sulfur, it is a very serious impurity from the viewpoint of a refiner since invariably it will act to deter, at least to some degree, almost every reaction that occurs as petroleum materials are refined. When nitrogen enters reformers, catalytic cracking units, hydrocrackers or polymerization units, the performace characteristics of these processes diminish significantly. The basic nitrogen compounds within the feedstocks tend to poison the catalysts used therein, particularly the acid and bifunctional catalyst systems. The impact of nitrogen concentrations down to levels of less than 100 parts per million will oftentimes kill cracking or hydrocracking activity, requiring the refiner to increase the severity of that operation in order to overcome the decrease in activity. Thus, substantial effort has been devoted to finding ways to inexpensively remove the nitrogen compounds from the feed streams before they enter the refining operations.
The techniques employed in the removal of such material from the feedstock have included, for example, chromatographic techniques wherein the basic nitrogen compounds are preferentially adsorbed onto solid supports such as silica, alumina or various grades of clay materials. In more recent years, as set forth in U.S. Pat. No. 4,090,951, syncrude feedstocks have been treated with materials selected from the group consisting of acid treated alumino-silicates, amorphous synethetic silica-alumina and crystalline silica-alumina cracking catalysts in order to provide a low nitrogen syncrude feedstock material. Other techniques have employed hydroprocessing procedures that use a hydrogen treatment at high hydrogen partial pressures over a catalyst such as metal sulfides. Extraction operations have also been reported in U.S. Pat. No. 4,071,435 using zine chloride followed by hydrocracking and in U.S. Pat. No. 4,159,940 using mineral acid extraction techniques.
Because adsorbing methods of the type described are inherently expensive, especially on fuel products which generally are not able to absorb much processing costs, hydroprocessing operations have been increasingly favored by refiners. Despite the high pressure vessels required in the hydroprocessing the technique is generally less expensive because there is no need to purchase clay and then discard it. Additionally, hydroprocessing operations tend to be continuous with only a minimum amount of down time. However such high pressure operations disadvantageously tend to be highly capital intensive, making them less competitive and correspondingly less desirable. Frequently, as in the first above-mentioned patent, the adsorbing technique is combined with a catalytic cracking operation in order to increase efficiencies of operation. Thereafter, the adsorbent is regenerated by removing from the spent adsorbent either thermally or by solvent extraction to recondition the adsorbent for reuse. As will be appreciated, the regeneration of the adsorbent is an additional cost factor that must be weighed against the cost of using a fresh supply of adsorber during the denitrogenation of the fuel feedstock.
In accordance with the present invention it has been found that the basic nitrogen compounds within fuel feedstock can be significantly reduced in a rapid, facile and economical manner by utilizing an adsorbing material which also is a fuel and can subsequently be utilized as a fuel after it has completed its adsorbing function. The utilization of such material obviates the problems associated with disposing of the adsorbent as an industrial product or the regeneration of the material for subsequent use. Not only does this eliminate the cost associated with such operations it also causes the cost of the adsorbent material to become insignificant since that material is itself used as a fuel. Such use of the adsorbent, of course, provides less incentive to recover that material for reuse as an adsorbent, particularly where the denitrogenation process takes place at locations where a large demand exists for the utilization of such a fuel and such demand is comparable to or exceeds its need as an adsorbent.
Advantageously, the removal of the basic nitrogen material from the feedstock by the process of the present invention avoids the procedures utilized hereforth and maximizes the value of this feedstock material for further processing. As can be appreciated, the utilization of the process of the present invention provides significant economic benefit since the material used as the adsorbing component can be readily, effectively and completely utilized after performing its adsorbing function by simply burning the material as a fuel in a conventional stationary boiler or other equivalent operation.
In addition to the economical factors associated with the process of the present invention, it will be noted that the efficiency of operation achieved by the technique employed herein can be superior to that achieved in accordance with the techniques reported in the above-referenced patents where the process provided a reduction of about 20 percent in the nitrogen concentration. The process utilized in accordance with the present invention provides nitrogen removal well above that 20 percent figure and, in fact, will show percent nitrogen removal up to about 85 percent and higher. Not only does the process of the present invention provide substantial high nitrogen removal but it performs this removal at low initial nitrogen concentrations, that is, at initial concentrations less than 1 percent, all without diminishing the removal efficiency. Thus, the nitrogen content of the treated feedstock is reduced to well below 1 percent and as low as 0.1 percent and less.
A further advantage of the present invention is that it also facilitates a reduction in the phenolic content of the feed stream concomitant with the denitrogenation thereby permitting an easier and more complete removal of the basic nitrogen compounds.
Other advantages will be in part obvious and in part pointed out more in detail hereinafter.
These and related advantages are achieved in accordance with the present invention by providing a new and improved method for reducing the concentration of basic nitrogen compounds in hydrocarbonaceous feedstock fluids. The method includes the steps of providing a solid particulate carbonaceous adsorbent/fuel material having active complexing sites on the surface thereof for complexing basic nitrogen compounds and contacting the solid adsorbent/fuel material with a hydrocarbonaceous feedstock fluid containing basic nitrogen compounds sufficiently to facilitate attraction of the basic nitrogen compounds to the complexing sites and the formation of complexes of those compounds on the surface of the solid adsorbent/fuel material. Subsequently, the solid particulate material and the complexes formed thereon are separated from the feedstock fluid to provide a hydrocarbonaceous fluid well suited for petroleum refining having a basic nitrogen compound concentration that is reduced by up to about 85 percent by weight and more.
A better understanding of this invention will be obtained from the following detailed description of the process including the several steps and the relation of one or more such steps with respect to each of the others and the products resulting therefrom possessing the features, characteristics, compositions, properties and relation of elements described and exemplified herein.